When successively printing from different originals, the sequentially formed stacks of sheets bearing the different printed results may be superimposed directly on the sheet receiving deck of the printing machine without the plane of separation between the individual stack portions being readily discernible. A variety of proposals have been made to distinguish these individual stack portions or runs. For example, a known pivotable-deck design has the sheet receiving deck pivoted slightly about its vertical axis at the end of each run so that the following sheets printed from the next original, or the partial stack formed thereof, will be deposited at a slight relative to the previously printed sheets. By pivoting the sheet receiving deck alternatively back and forth, the individual stack portions may be distinguished readily. However, this design usually does not include a deck which may be lowered. Also, the design is disadvantageous in that it requires additional structure for the sole purpose of marking the different runs. Thus, it is necessary to provide both for the pivoting mounting of the sheet receiving deck and for a mechanism to impart pivoting movement to the deck.
Also, it has been known to mark individual stack portions by inserting paper slips between them. This solution is disadvantageous in that the stack in its entirety may be deposited out of angle, and additional structure, i.e. slip insertion apparatus, must be provided at a suitable position in the machine, which may lead to space problems. Also, that solution may create particular difficulties in case the sheet receiving deck is not lowered gradually, so that the top of the stack will be at different levels at different times.
One of the objects of the present invention is to improve on the apparatus mentioned above so that individual runs or stack portions of sheets of paper deposited on the sheet receiving deck of a machine may be marked clearly without using either a pivoting deck or any separate slip inserting mechanism. This object is to be attained by technical and a design as simple and inexpensive as possible, i.e. utilizing as far as possible constructional elements already available on the printing machine.